Nitrocellulose manufacture



Patented June 13, 1933 UNITED STATES PATENT OFFICE MILTON O. SOHUR, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY, OF

BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE NITROOELLULOSE MANUFACTURE No Drawing. Application filed May 31,

Ihis invention is directed to the manufacture of nitrocelluloses, and more particularly to a process in which the cellulose fiber used as a raw material is a wood pulp.

Innitrat-ing cotton linters in accordance with customary practice, the nitrating acid used is a mixture in which the ratio of nitric acid to sulphuric acid is almost always less than one to two. If, with such a raw material, this ratio is increased, nothing much is gained even though the nitric acid component of the nitrating acid is by far more expensive than the sulphuric acid component. On the other hand, I have discovered that the use of a nitrating acid much richer in nitric acid than that customarily employed with cotton linters is highly desirable when using wood pulp, especially unbeaten pulp, in the form of sheets as a raw material for nitrocellulose manufacture. This desirability resides both in the ability of the nitric-acid-rich nitrating acid to maintain the sheets intact throughout the nitrating operation, so that the nitrated sheets may be handled as such through afternitration treatments and finally be stored or 'marketed without-tending to crumble, and good yields and reasonably low acid retention obtain even when the temperature of the bath of nitrating acid is as high as 30 to 40 (1, or even higher, under which conditions nitration may be effected in a reasonable period of time. These results are in marked contrast to those obtained when the nitrating acid is of the composition customarily employed with cotton linters, in which case the nitrated sheetsof wood pulp tend to crumble, especially when the nitrating acid is kept at 80 tov 40 (1, or higher, the acid retention is high, and the yields are poor, evidently owing to side reactions accompanying the main nitrating reaction and acid hydrolysis occurring when the sheets are drowned in water. In accordance with the present invention, I employ a nitrating acid in which the ratio of nitric acid to sulphuric 1930. Serial No. 458,887.

acid is at least about one to two when using wood pulp in sheet form as the raw material for nitrocellulose manufacture. I cite the minimum ratio for the reason that if it is adhered to or increased, comparatively good results are obtained, but if it is materially reduced, the results are very disappointing.

The utility of my invention is at once apparent when it is considered that not only does it make available wood pulp for use as a raw material for nitration, but further that it comprehends such wood pulp iii a form or condition as it customarily appears on the market. Thus, manufacturers of wood pulp are generally equipped with driers over which the processed pulp in unbeaten condition is run to produce comparatively thick sheets, known as drier sheets. Not only is the production ofsuch sheets desirable because they are compact, easy to handle, store, and ship, and because pulp driers may be built as large units capable of handling at low cost 200 or more tons of dry fiber per day, but further because they lend themselves well to certain chemical treatments. For instance, they are convertible as such to alkali cellulose, such as is used in the manufacture of artificial silk by the viscose-rayon process; and they are hence in demand for this purpose. They lend themselves even better for nitration, as in such latter case they may be maintained in sheet form to the finished product. Again, because of their compactness, the ratio of nitrating acid to fiber during nitration may be low in comparisonwith that necessary in the nitration of cotton linters, so that the size of the nitration apparatus and the volume of expensive acid in process for a given production of nitrocellulose may be kept comparatively small.

In order to appreciate the results secured by applying the principles of the present invention, various specific examples falling within the purview of the present invention will now be given; and the results obtained therein will be compared with those secured when these principles are departed from. In all these examples, I employ drier sheets composed of an unbeaten, highly refined wood pulp of high alpha cellulose content and pure whiteness, as such pulp yields nitrocelluloses having characteristics comparing favorably with those produced from the best grade cotton linters. These drier sheets were 0.040 inches thick and weighed about 450 grams per square meter.

Example l.-The drier sheets were steeped for six hours in a bath of nitrating acid at 25 (3., consisting of 16% water, 42% nitric acid, and 42% sulphuric acid. They were then' successively drained, drowned, stabilized, and washed in the usual manner. A yield of 157.2% of nitrated product having a nitrogen content of 11.28% was realized, this yield representing 100% of the theoretical value on the basis of the nitrogen content obtained. The acid retention was 1.6 pounds of acid per pound of nitrocellulose. Example ll.The procedure of this example was like that of the preceding example, except that the nitrating acid consisted of 17% water, 33.2% nitric acid, 49.8% sulphuric acid, and was at 28 C. The yield obtained was 156.5%, the nitrogen content 11.20%, and the acid retention 1.45.

Example lIl.Following the procedure of the foregoingexample, with a nitrating acid consisting of 17.0% water, 27.7% nitric acid, and 55.3% sulphuric acid, the results were: yield, 155.4%; nitrogen content,

" 11.35%; acid retention 1.71.

All of the foregoing procedures, in which it will be noted that the nitrating acid used contained nitric acid and sulphuric acid in the ratio of one to two or higher, yielded sheets of nitrocellulose in firm and intact condition. When this ratio was decreased, the results were comparatively poor as can be seen from the following example:

Example IV.-The sheets were steeped for six hours in a bath of nitrating acid at 25 C., consisting of 17.0% water, 23.8% nitric acid, and 59.2% sulphuric acid. The resulting nitrocellulose was subjected to the usual after-nitration treatments. The yield obtained was 150.9%; the nitrogen content 11.44%; and theacid retention 2.50. The sheets of nitrocellulose were so soft and weak that great care had to be exercised in handling them; otherwise they tended to fallto pieces.

When the four examples of procedure hereinbefore given were carried out with the temperature of the bath of nitrating acid at 40 0., in all cases the yield dropped, and in all cases but the first the acid retention went up and the sheets tended to become weaker. The time necessary to effect complete reaction, however, was less than four hours in every case. In those cases, however,wherethe ratio of nitric acid to sulphuric acid was 1 to 2 or higher, the results obtained at 40 C. for four hours were not very much worse than those obtained at 25 to 28 C. for six hours; but in the case where the ratio of nitric acid to sulphuric acid was less than 1 to 2, the results obtained at 40 C. were exceedingly poor. Thus, with an acid of the composition given in Example IV, the yield dropped from 150.9 to 95, and the acid retention rose from 2.50 to 5.18. While, as in the examples hereinbefore given, the wood pulpis preferably used in the form of comparatively thick sheets and in unbeaten condition, nevertheless the principles of the present invention are applicable when such pulp is used in the form of tissues'or papers made from the beater pulp. When undergoing nitration, the sheets, if of comparatively large area, may be submersed in the nitrating acid while supported in frames or on racks or are sus- .pended fromrods or clamps, preferably being maintained in spaced, parallel relation throughout the nitrating operation so that the nitrating acid will contact uniformly with all the surface presented, to ensure a uniform reaction. The sheets may, however, be cut into pieces of small size, as distinguished from pulp or cotton linters in bulk form, in which case the procedure followed beaten pulp. When undergoing nitration,

treatments may be more or less analogous to those customarily employed in the industry.

In giving the composition of the nitrating acid, it is necessary to set forth only the ratio of nitric acid to sulphuric acid, for it is well known in the art that in order to arrive at a nitrocellulose of a given nitrogen content, a nitrating acid of a definite nitric acid to sulphuric acid ratio should have a predee termined water content. As the ratio of one acid to the other varies, the water content necessary to produce a nitrocellulose of the same given nitrogen content may vary within relatively narrowlimits. Generallyspeak:

ing, the amount of water present in the ni- :z

trating acids of the present invention may be from, say, 12% to 23%, depending upon the nitrogen content and other characteristics desired in the nitrocellulose, but it is to be understood that the range of water content may also vary, depending upon many factors, including ratio of one acid to the other,

the ratio of 'nitric to sulphuric acid is appreciably greater than 1 to 2 and at a temperature of about 25 C. to 40 C.

2. A process which comprises treating sheets of wood pul with a. nitrating acid in which the ratio 0. nitric to sulphuric acid is appreciably greater than 1 to 2 and at a temperature of about 25 C to 40 C.

3. A process which comprises steeping comparatively thick sheets of wood pulp in a nitrating acid in which the ratio of nitric to sulphuric acid is appreciably greater than 1 to 2 and at a temperature of about 25 C. to 40 C.

4. A process which comprises steeping comparatively thick sheets of wood pulp in spaced, parallel relation in a nitrating acid in which the ratio of nitric to sulphuric acid is appreciably greater than 1 to 2, until the sheets have been substantially uniformly nitrated and at a temperature of about 25 C. to 40 C.

5. A process which comprises treating comparatively thick sheets of highly refined wood pulp with a nitrating acid in which the ratio of nitric to sulphuric acid is appreciably greater than 1 to 2 and at a temperature of about 25 C. to 40 C.

6. A process which comprises treating .sheets of wood pulp with a nitrating acid in which the ratio of nitric to sulphuric acid is not less than 1 to 2 and whose water con-' tent may be from, say 12% to 23%.

7 A process which comprises treating wood pulp with a nitrating acid in which the ratio of nitric to sulphuric acid is not less than 1 to 2 and whose water content is from 12% to 23%. f

8. A process which comprises treating sheets of substantially unbeaten wood pulp with a nitrating acid in which the ratio of nitric to sulphuric acid is appreciably greator than 1 to 2 and at a temperature of about 25 C. to 40 C.

9. A process which comprises treating sheets of substantially unbeaten, refined wood pulp with a nitrating acid in which the ratio of nitric to sulphuric acid is not less than 1 to 2 and whose Water content is from 12% to 23%.

10. A process which comprises treating sheets of wood pulp having a thickness of about 0.040 inches and weighing about 450 grams per square meter with a nitrating acid in which the ratio of nitric to sulphuric acid is appreciably greater than 1 to 2 and at a temperature of about 25 C. to 40 C.

11. A process which comprises treating sheets of wood pulp having a thickness of about 0.040 inches and weighing about 450 grams per square meter with a nitrating acid in which the ratio of nitric to sulphuric acid is not less than 1 to 2 and whose water content is from 12% to 23%.

12. -A process which comprises treating sheets-of substantially unbeaten, refined Wood pulp having a thickness of about 0.040 inches and weighing about 450 grams per square meter with a nitrating acid in which the ratio of nitric to sulphuric acid is appreciably greater than 1 to 2 and at a temperature of about 25 C. to 40 U.

13. A process which comprises treating sheets of substantially unbeaten, refined wood pulp having a thickness of about 0.040 inches signature.

MILTON O. SCHUR.

CERTIFICATE or CORRECTION.

men: No. 1,914,302. June 13, 1933.

MILTON 0. SCHUR.

It is hereby certified that error appears in the printed specification 0! the above numbered patent requiring correction as follows: Page 2, line 95 strike 7 out the words "beatenpulp. When undergoing nitration, "and insert instead during the nitration and the after-nitration; and that the said Letters Patent should 'be read with this correction therein that the same may conform to the'record of the ease in the Patent Office.

Signed'and sealed this 22nd day of January, A. D. .1935.

Leslie Frazer (Seal) Acting Commissioner of Paienta. 

